1. Field of the Invention
The present invention relates to a display device using a liquid crystal panel.
2. Description of the Related Art
In some conventional display devices using liquid crystal panels, an EL panel is used as a backlight for a liquid crystal panel a, as shown in FIG. 5. The liquid crystal panel a is connected with electrodes of a circuit board b by an LCD connector. Since the liquid crystal panel a has a large number of pins, a relatively large area is required for wiring. Usually, the wiring is placed under the liquid crystal panel a. Therefore, an EL driver circuit c for driving the EL panel is not placed under the liquid crystal panel a but in a remote position on the circuit board b. Lead wires d are brought out from the EL panel for connection with the EL driver circuit c.
When the EL driver circuit c is placed on the circuit board b remote from the liquid crystal panel a as mentioned above, space must be secured on the circuit board b for this purpose. This makes the circuit board b bulky. Furthermore, the EL panel is driven with a high driving voltage and so a step-up circuit is employed. This results in considerably severe RF switching noise which affects the surroundings from the lead wires d. For example, in the case of an instrument for measuring minute electrical currents such as a photometer, the noise may deteriorate the performance of the instrument. Consequently, the EL panel cannot be placed close to the minute current detection portion or a high-gain amplifier unless any countermeasure is taken. In this manner, limitations are placed on the placement of the EL driver circuit.
When the output voltage from the step-up circuit is coupled to the EL panel by the lead wires d, if the step-up circuit is placed remote from the EL panel, the effect of noise varies according to the manner in which leads are wired. As a result, shielded wires must be used or another countermeasure is necessary. In this regard, there are many problems associated with such arrangements.
It is an object of the present invention to provide a display device free of the foregoing problems.
Accordingly, a display device in accordance with the present invention includes a liquid crystal panel spaced a given or set distance from a circuit board and an EL panel for illuminating the liquid crystal panel located behind the liquid crystal panel. Furthermore, an EL circuit board having an EL driver circuit thereon is located behind the EL panel. In this embodiment, the EL panel and EL circuit board are placed close to each other, and the surroundings are prevented from being adversely affected by noise generated by the EL driver circuit.
The space between the liquid crystal panel and the circuit board is maintained by a support member. Preferably, the liquid crystal panel is held against the circuit board by a holddown frame. This structure facilitates maintaining the spacing between the liquid crystal panel and the circuit board.
Preferably, a shielding plate is mounted on the circuit board and opposite the EL panel to cut off noise produced by the EL driver circuit. This structure can prevent the surroundings from being adversely affected by noise.
It is also desirable that the EL circuit board be electrically connected with the shielding plate. In addition, the EL circuit board is preferably connected via a contact member with power-supply electrodes on the circuit board, the electrodes being exposed from the shielding plate. Moreover, the EL circuit board is preferably connected via the contact member with electrodes used for supplying control signals, the electrodes being exposed from the shielding plate. This structure facilitates making connections and assembling the display device.
Other objects and features of the invention will appear in the course of the description thereof, which follows.